1. Field of the Invention
The present invention relates to an optical pickup servo-control apparatus for use with an optical disc recording and/or reproducing apparatus.
2. Description of the Related Art
It is required for a recording and/or reproducing apparatus (hereinafter, referred to as a recording/reproducing apparatus) to attain a precise recording/reproduction of the information stored on an optical disc such as a CD (Compact Disc) or a DVD (Digital Versatile Disc). Accordingly, such a recording/reproducing apparatus generally employs a servo-control apparatus such as a tracking or focusing servo system to provide a controlled reading position for the optical pickup for reading recorded information.
A servo-control technique employed in such an apparatus makes use of a read RF signal from the optical pickup to generate an error signal. It is necessary to provide an appropriately gain-controlled voltage for the signal to be supplied to an error signal generator section for generating the error signal. Thus, the apparatus is generally provided with an automatic gain control (AGC) circuit for providing a controlled gain in accordance with an input signal. In particular, the technique for performing the automatic gain control using a disturbance source is useful since it provides a precise measurement of gain control for the apparatus. In addition, the technique can perform the automatic gain control before a recording and/or reproducing operation to provide a gain set point for the servo system, thereby making it possible to continue stabilized servo-control thereafter.
A disc recording/reproducing apparatus including such an automatic gain control circuit as described above can best provide a controlled gain by performing automatic control each time information is read and/or recorded on the disc. However, this requires a certain amount of time for the apparatus to complete the automatic gain control and then read or record information on the disc. In this regard, there is a method available for shortening the length of set-up time required to complete the automatic gain control. According to the method, the automatically controlled gain provided upon reading or recording information on the disc is stored to be used again in the following reading or recording. Such a method for controlling a disc recording/reproducing apparatus is disclosed, for example, in Japanese Patent Laid-Open Publication Kokai No. H7-130087.
However, in many cases, characteristics of discs and service conditions of recording/reproducing apparatuses are different each time they are used as well as service environments such as ambient temperature and humidity. Thus, the stored control gain is not always most suitable. For example, when a disc is once removed from a recording/reproducing apparatus and then re-loaded to the apparatus, a slight variation in a loading condition would require a different optimum control gain. Thus, in some cases, this would result in a decrease in servo-control performance or deterioration in quality of reading or recording.
The present invention has been made in view of the aforementioned problems. It is an object of the present invention to provide a servo control apparatus which can shorten the set-up time and perform stabilized servo control with high accuracy.
To achieve the object, according to the present invention, there is provided a servo control apparatus for use with an optical disc player for reading and/or recording information on a storage medium, which comprises an adjustment section for performing coarse and fine adjustment of a servo loop gain in accordance with the storage medium loaded in the player; a memory for storing a gain adjustment value in the adjustment section; a discriminator for determining, upon one of reading and recording information on the storage medium, that the storage medium has already been subjected to the coarse and fine adjustment of the servo loop gain by the adjustment section; and a controller for allowing the adjustment section to perform the fine adjustment of the servo loop gain in accordance with the gain adjustment value stored in the memory when the discriminator has determined that the storage medium has already been subjected to the coarse and fine adjustment of the servo loop gain.